Guns have many sporting applications. For example, shotgun shooting is a multi-event Olympic sport that is growing in popularity. Competitive rifle shooting is also a well established sporting activity.
The least powerful guns used in competitive shooting are airguns. These fire a pellet that is powered by compressed air. The range of a fired pellet is typically 30 m or less, and so airguns are only suitable for short range shooting.
Guns with longer ranges fire ammunition powered by gun powder. A shotgun fires cartridges in which a plurality of pellets are fired in a spread pattern from the gun. Shotguns are typically used for shooting targets in the air at a range of about 50 m. Rifles fire a single bullet and have a much longer range than shotguns. For example, a .308 Winchester rifle may hit a target 1000 m away.
Shotguns are typically provided with two barrels. In an over-and-under configuration, one barrel is directly above the other in use. In a side-by-side configuration, the barrels are horizontally adjacent to each other in use. Shotguns with more than two barrels are also known, as are rifles with a plurality of barrels.
The accuracy of a gun, in particular shotguns and rifles that are required to operate at relatively long ranges, is a critical performance measure.
For every gun, a factor that influences its accuracy is the straightness, and smoothness, of the gun barrel. The accuracy of a shot, and the consistency of the placement of the shot, both improve as the straightness and smoothness of a barrel are increased.
The usability of a gun is also highly influential on its accuracy. In particular with shotguns, a gun with a large perceived recoil requires the user to compensate for the effect of the recoil with their shooting technique. A large perceived recoil is also unpleasant for the user and requires the user to recover from the recoil prior to firing the gun again.
In known manufacturing techniques of guns with more than one barrel, each barrel is formed separately. Each barrel is formed by drilling a single hole through a metal block and then forming the outside of the barrel, for example, by turning the barrel on a lathe. The two formed barrels are then soldered together with the barrels spaced apart by a central rib.
A problem with such known manufacturing techniques is that the soldering operation heat treats the metal barrels and thereby degrades their straightness. This reduces the accuracy of each barrel.
A further problem is that the rib imposes a minimum spacing of the barrels. To compensate for the reduced accuracy introduced by the barrel spacing, the barrels are angled towards each other. This is necessary to ensure that, for a particular aim of the gun, projectiles fired from each barrel will be fired into the same position at a pre-determined distance from the gun. However, the angling of the barrels towards each other increases the perceived recoil from the gun. since the angling of the barrels imparts a sideways momentum on the butt of the gun after the gun has been fired.
Accordingly, a number of problems exist with gun barrels for multi-barrelled guns that have been manufactured according to known techniques.